Method of heat treatment, separation, and coking coal



particles to effect separation thereof.

be accomplished by any of various conventional devices 4 for separatingdry materials of different densties.

United States Patent F METHOD OF HEAT TREATMENT, SEPARATION. AND COKINGCOAL Frederic William Jung, Kansas City, Mo.

Application May 15, 1956, Serial No. 585,073

7 Claims. (Cl. 202-25) This invention relates to an improved method oftreating coal, and more particularly to a method of separating high orlow vitrain co'als from non-vitrain types. It is an object of theinvention to provide an improved method of this character.

Various applications of coal make it desirable that vitrain in coal beseparated from other forms or constituents of coal which are containedin a mixture as commonly found in nature. One such application is inobtaining coal for coking purposes from a coal supply which has poorcoking characteristics. Another application concerns the separation ofcertain valuable mineral content which may be incorporated exclusivelyor primarily in the vitrain. The present invention relates to the basicseparation of vitrain from other forms of coal and to the furthermanipulation of the separated coal forms in various applications.

The method which constitutes the present invention may be employed notonly to separate the high vitrain coals from other forms but may furtherbe employed to separate low vitrain coals from non-vitrain coals.Basically the separation method includes crushing the coal to anadvantageous particle size, heating the coal in an inert atmosphere toa. temperature at which the vitrain begins to soften, but below thattemperature at which the vitrain reaches maximum fluidity, to causeswelling of the Vitrain particles and thereby to reduce their efiectivedensity, agitating the crushed mixture to prevent agglomeration, andutilizing the resulting difference in density of the mixed The latterstep may Accordingly it is another object of the invention to provide animproved method of separating high vitrain coal from a mixture ofvarious coal forms.

It is another object of the invention to provide an improved method ofseparating a mixture of coal forms into three groups, one containinghigh vitrain coal, one containing low vitrain coal, and the othercontaining nonvitrain coal.

It is another object of the invention to provide an improved method forobtaining coal of good coking properties from coal having poor cokingproperties.

It is another object of the invention to provide an improved method ofseparating valuable mineral-bearing coal components from a mixture ofvarious forms of coal.

This invention, together with further objects and advantages thereof,will best be understood by reference to the following description takenin connection with the accompanying drawing and its scope will bepointed out in the. appended claims.

In the drawing, in which like parts are designated by like numerals,Figure 1 is a generalized flow diagram of the method basicallyconstituting the present invention; and

Fig. 2 is a diagram showing a typical relationship between fluidity andtemperature for vitrain-containing coal which is subjected toprogressive beating out of air.

, 2,803,587 Patented Aug. 20, 1957 Coal deposits very commonly occur inbanded or striped formation in which there are layers of differentpetrographic forms of coal resulting from the depositing of differentforms of organic material or from the existence of different conditionsin prehistoric times. The various types of coal are frequently referredto as and are herein termed, fusain, vitrain, clarain and durain.Vitrain is sometimes referred to as bright coal or anthraxylon. Clarainis sometimes referred to as semisplint coal or translucent attritus, anddurain is sometimes referred to a'splint coal or opaque attritus.

Of these four forms of coal it is the vitrain which serves as theadhesive or cement which softens and holds the other forms of coaltogether when pulverized coal is subjected to a coking process. If thereis an insuflicient percentage of vitrain the coal will not coke togetherproperly, the result being a large percentage of loose coal particlesaccompanied by small pebbles of coke. Accordingly, coal deposits inwhich the vitrain content is too low for good coking are considered asmarginal or non-coking coals. When coal, for example, contains vitrain,it is considered high grade coking coal, whereas 20% vitrain is too lowfor good coking. One and purpose of the method which constitutes thepresent invention is to increase the percentage of vitrain coal in amixture, such that good coking coal can be obtained from marginal ornon-coking coal. This may be accomplished by removing the vitrain coal,and, if desired, coal forms having small amounts of vitrain incorporatedtherein, after which these may be mixed with a smaller percentage ofother forms of coal than was contained in the original mixture. Themethod is adapted not only to good quality coals but to sub-bituminousand lignitic coals, and where the term coal is employed herein in itsgeneral sense it is intended to include there lower ranks of coal.

The first step in the method which constitutes the present invention isthe pulverizing of the coal to a desired particle size. In general ithas been found that pulverizing the coal to a particle size ofapproximately of an inch, as obtained with a IO-mesh (per inch) screen,is satisfactory and permits successful application of the method. Morebasically, however, the particle size may be equal to but not greaterthan the thickness of the layers of vitrain in the banded coal deposit.For example, if the majority of the vitrain layers in a given depositmeasures at least /8 of an inch in thickness, the particle size obtainedby pulverization should not exceed inch. By following this basic rule,advantage is taken of the tendency of the coal to separate at the planesof jointure between coal forms. It will readily be seen that if thelayers of vitrain are primarily of an inch thick and the coal ispulverized to a particle size of of an inch, very few particles of coalwill include both a substantial quantity of vitrain and a substantialquantity of another form of coal such as fusain, clarain or durain.Rather, the layered coal will tend to break, during pulverization, atthe planes of jointure such that the vitrain will exist primarily inparticles of pure vitrain.

Accordingly, banded coal should be pulverized to a particle size whichis substantially equal to or less than the minimum thickness of thevitrain bands. As indicated above, generally satisfactory results areobtained if the coal is pulverized to a particle size of of an inch.Pulverization of the coal can be accomplished by any of the conventionalforms of coal crushers or pulverizers. It is desirable that excessivefines be avoided for reasons which will subsequently become apparent.

After the coal mixture has been pulverized to the desired particle size,it is heated in an inert atmosphere to a temperature slightly above thepoint of initial softening of the vitrain and well below the point ofmaximum fluidity of the vitrain. Because of the fact that no two 'to thepulverized coal.

coals are exactly the same, even though they may be of the samerecognized form, no specific, universal temperature limits can be givenwhich can be employed "blindly withfull assurance of success. Forexample,

the initial softening point may generally vary from 350 C. to 450 C. andeven outside these temperatures for vitrain from different sources. Itis recommended that coal from a given source be subjected to tests todetermine the initial softening point and the point of maximum fluidity.The well known Gieseler apparatus and the Davis plastometer are suitablefor this purpose. Fig.

2 shows a typical curve obtainable from the use of the first-named testapparatus. In the illustrated diagram, point A is the point of initialsoftening, point B is the point of maximum fluidity, and point C is thesetting point. It will be noted that there is a reasonable temperaturerange between points A and B in the illustrated curve. In some instancesthis range may be less than in others, such that the temperature must bemore closely controlled in the process.

substantially reduced. Such expansion and consequent reduction ineffective density occurs when the vitrain is heated above its initialsoftening point because of the increased evolution of volatilized matterat such temperatures. Heating of the coil to a substantially highertemperature, at which the vitrain reaches or closely approaches itspoint of maximum fluidity, is to be avoided since this may causeagglomeration of the melted vitrain particles with each other, and, withother nonsoftened particles of other forms of coal. The true limitationsof this method are as defined immediately above, namely, that thevitrain be heated to the temperature immediately above its initialsoftening point but below its point of maximum fluidity.

It is also desirable that the mixture be mechanically agitated while thecoal particles are at the prescribed elevated temperature to reduce oreliminate agglomeration. Apparatus for accomplishing such agitation ofthe pulverized coal is commonly known in the art, typical examples beingthe Disco (Lesher) oxidizing stoves and the Wiener and Hayes rotaryretorts. Mechanical agitation of the particles should, of course,continue throughout the time that the particles are maintained atelevated temperatures.

As indicated above, the pulverized coal should be maintained in an inertatmosphere while it is at these elevated temperatures for reasons wellrecognized in the art. Primarily the inert atmosphere should benonoxidizing, in order to prevent combustion and/or oxidation andgeneral deterioration of the various forms of coal. Secondarily theatmosphere employed should contain no other elements or components whichwill tend to combine with the coal and produce characteristics which areundesirable in a given application. It has been found that properlycontrolled combustion gases form a suitable inert atmosphere forprotecting the coal while it is maintained at elevated temperatures.Such combustion gases may be obtained from the heating process itselfand may actually carry the desired heat However, other forms of inertatmosphere may well be employed where economic conditions and otherfactors so dictate. It will of course be understood that the coal shouldbe maintained in an inert atmosphere as long as it is maintained atelevated temperatures. i

It has been found that where the particle size is on the order of of aninch, the desired swelling and consequent reduction in apparent densityof the vitrain particles takes place almost immediately upon subjectionof the coal particles to the hot inert gases. This of course assumesthat the drum, tray or other device or medium which may support thepulverized coal is already hot. In other words, with coal particles ofthis size the required period of heating to obtain the desired swellingof the vitrain particles is governed almost exclusively by the initialtemperature and thermal capacity of the supporting medium. Where alarger particle size is employed, a longer heating period istheoretically required, but as a practical matter the required time maystill be determined primarily by the apparatus rather than by theparticle size.

Another factor affecting the required heating time is the moisturecontent of the coal. As will readily be understood by those skilled inthe art, if a substantial amount of moisture is incorporated in the coal(lignitic coals frequently containing 30% moisture) this moisture mustbe evaporated before the coal particles can be heated to a temperaturesubstantially above the boiling point of Water. This of course increasesthe necessary heating period and amount of heat required.

In some applications of coal it is desired that volatile matter in thecoal be reduced to some predetermined level. The driving off of suchvolatiles can readily be accomplished as a part of this method. In suchcase it may be desired that the coal be maintained within the criticaltemperature range, defined above, for a longer period of time, or it maybe desired that the coal be maintained at a somewhat lower temperaturefor an appreciable period of time to drive off the volatiles before orafter the coal is raised to a temperature within the above definedrange. Since the removal of volatiles of coal is well known in the art,particularly in connection with coking and charring processes, thissupplementary function of the method which constitutes the presentinvention is not described in further detail herein.

In order to obtain maximum use of a coal heating unit and to minimizeoxidation it is desirable to heat the coal rapidly. This produces atransient condition wherein fines will be heated to an objectionablyhigh temperature while the particles of basic size are reaching thedesired temperature. For this and other reasons excessive fines shouldbe avoided, as suggested above.

In some applications of this method it may be desired that the .coalafter being treated to this point be cooled such, that it may be storedor transported. It will of course be apparent that the coal should becooled while remaining in an inert atmosphere, to permit protectiveabsorption of inert gases by reactive new pore surface, and while beingfurther mechanically agitated, if needed, to prevent agglomeration.Cooling of the coal may be accomplished in any suitable manner, but ispreferably effected outside the heating apparatus as a part of acontinuous process in order to obtain maximum use of equipment.

After the treated coal has been cooled, such that it may be exposed tonormal atmosphere, the expanded vitrain particles, being of lessereffective density than the particles of other forms of coal included inthe mixture, may readily be separated therefrom by any of various wellknown separating devices. Preferably a dry separation process isemployed, and among the devices which may be used satisfactorily in thisstep of the method are cyclone separators, air separation tables such asthose of Roberts and Schaefer or Sutton, Steele & Steele, and beltseparators. Since these devices and their principles of operation arewell known in the art, they are not described in detail herein. For thepurpose of disclosing the present invention it is sufiicient to indicatethat such devices are capable of separating low density dry materialsfrom higher density materials. Accordingly they can successfullyseparate the expanded vitrain particles, having low effective density,

from the remaining coal particles.

In some applications of the present invention it may be desired that theheated coal particles be fed directly to utilization stations withoutbeing cooled. In such applications the loss of heat and the time delayattending the cooling of the pulverized coal can be avoided bysubjecting the treated coal particles to a dry separation process whilestill hot and while still being maintained in an inert atmosphere. It isrequired simply that the separation apparatus be incorporated in thesame enclosure or a continuation thereof and that it be continuouslymaintained in an inert atmosphere. After separation, the vitrainparticles or the remaining coal particles, or both, may be fed directlyto their ultimate utilization stations without cooling.

Apparatus incorporating a fluidized column may be utilized for bothheating and separating. Such apparatus is recommended for use in thismethod as being rapid and efficient, but it should be recognized that itrequires delicate control for satisfactory results.

The method as described above has been presented primarily as a methodof separating vitrain from other forms of coal. It frequently occursthat these other forms of coal may have incorporated therein a small butsignificant percentage of vitrain. Clarain, for example, generallycontains some substantial amount of the essential component, vit-rinite,of vitrain. Those particles which thus contain a significant amount ofvitrain will be caused to swell by the heating process in much the samemanner as the pure or high vitrain particles but to a much lesserextent. Accordingly, the apparent density of these heated particles willbe significantly less than the non-vitrain coal particles but theirdensity will not be reduced as much as the pure vitrain particles. Thelessening in apparent density of these coal particles in accordance withthe percentage of vitrain contained therein may be employed, however, toseparate these particles of intermediate density from the pure vitrainparticles and from the non-vitrain particles by the same dry separationapparatus suggested above. By this means three groups of coal result,namely, substantially pure vitrain, other forms of coal containing asignificant percentage of vitrain, and a third group consisting ofnon-vitrain coals.

The same separation step may be employed, if desired, to clean the coalof unaltered or but slightly altered pyritic matter and ash-formingminerals freed in the pulverization, these foreign materials beingsubstantially heavier than the coal forms and therefore being readilyseparable from coal by the same apparatus that separates the treatedcoal.

As indicated above, coal which is to be used in a coking process shouldcontain a certain minimum percentage of vitrain since the latter is theparticular form of coal which provides the adhesive or bonding power toeffect coking. The method described above may be used to substantialadvantage in obtaining good coking coals from poor coking coal since itseparates the vitrain particles from the nonvitrain particles. Aftersuch separation the vitrain particles may be tested for purity and maybe mixed, if desired, with a given percentage of non-vitrain coalparticles or low vitrain coal particles, or both, to produce the desiredratio of vitrain to non-vitrain coals. If preferred, a good cokingmixture of reasonably accurate proportions can be obtained directly bycontrolling the separation of the treated coals such that the vitrainand desired percentage of low vitrain and/ or non-vitrain coals areseparated as a group from the residue of low vitrain and/or non-vitraincoals. It is of course necessary in any case that the original coalsupply contain a significant percentage of vitrain in order for themethod to be practical.

Another application of the described method relates to the separation ofvaluable minerals which are most commonly present in vitrain and not inother coal forms. Frequently, germanium or uranium oxide is extractedfrom coal simply by controlled burning of the coal and then treating theashes to recover these valuable minerals. The above described method canbe employed to great advantage as a preliminary to such a process, sincethese minerals are concentrated primarily in vitrain when present incoal or lignite. If the vitrain is first. separated from the other coalforms according to the method described above, the vitrain coal can beburned separately, with the result that a much smaller quantity of ashneed be treated to recover all or practically all of these valuableminerals than would be required if the entire supply of coal were burnedtogether.

In accordance with one practical method of employing the method whichconstitutes the present invention, the non-vitrain coals, or a portionthereof, which are obtained from the process may be burned to supply theheat necessary to eifect the separation of the coals. Heat transferapparatus may be employed, or the combustion gases, properly controlled,may be used directly to supply the necessary heat.

It will be understood that after dry separation of the vitrainparticles, they may be used in any one of the several further stepsabove described, or a portion of the vitrain particles may be used inone of such steps and one or more remaining portions may be used in oneor more of the other steps separately. In other words, the vitrainparticles may be used in the mineral recovery or in the compounding of acoking mixture or for supplying heat to the coal from the pulverizer.

It will also be understood therefore that the flow diagram of Figure 1indicates that the three steps may be carried out either alternately orany two or three may be carried out simultaneously.

I claim:

1. The method of separating high vitrain coal from a banded mixture ofcoal forms which comprises crushing said mixture to particle size notgreater than the minimum thickness of the included vitrain layers,heating the crushed mixture while in an inert atmosphere to atemperature above the initial softening point of the included vitrainand below the point of maximum fluidity thereof thereby causing swellingof said high vitrain particles and consequent reduction in effectivedensity thereof, mechanically agitating said crushed mixture while atelevated temperature to prevent agglomeration, and utilizing theresulting difference in density of the mixed particles to effectseparation thereof.

2. The method of separating high vitrain coal from a banded mixture ofcoal forms which comprises crushing said mixture to particle size notgreater than the minimum thickness of the included vitrain layers,heating the crushed mixture while in an inert atmosphere to atemperature above the initial softening point of the included vitrainand below the point of maximum. fluidity thereof thereby causingswelling of said high vitrain particles and consequent reduction inelfective density thereof, agitating said crushed mixture while atelevated temperature to prevent agglomeration, and separating the highvitrain particles from the remaining particles, utilizing thedifferences in densities of the mixed particles to effect suchseparation.

3. The method of separating high vitrain coal from a banded mixture ofcoal forms which comprises crushing said mixture to particle size notgreater than the minimum thickness of the included vitrain layers,heating the crushed mixture while in an inert atmosphere to a temperature above the initial softening point of the included vitrain andbelow the point of maximum fluidity thereof thereby causing swelling ofsaid high vitrain particles and consequent reduction in effectivedensity thereof, mechanically agitating said crushed mixture while atelevated temperature to prevent agglomeration, cooling the mixture in aninert atmosphere, and separating the high vitrain particles from theremaining particles, and utilizing the differences in densities of themixed particles to effect such separation.

. 4, The method of separating high vitrain coal from a banded mixture ofcoal forms which comprises crushing said mixture to particle size notgreater than the minimum thickness of the included vitrain layers,heating the crushed mixture While in an inert atmosphere to atemperature above the initial softening point of the included vitrainand below the point of maximum fluidity thereof thereby causing swellingof said high vitrain par ticles and consequent reduction in effectivedensity thereof, agitating said crushed mixture while at elevatedtemperature to prevent agglomeration, separating the high vitrainparticles from the remaining particles, utilizing the diflerences indensities of the mixed particles to efi'ect such separation andrecovering included minerals from the separated high vitrain particles.

5. The method of separating high vitrain coal from a banded mixture ofcoal forms which comprises crushing said mixture to particle size notgreater than the mini mum thickness of the included vitrain layers,heating the crushed mixture while in an inert atmosphere to atemperature above the initial softening point of the included vitrainand below the point of maximum fluidity thereof thereby causing swellingof said high vitrain particles and consequent reduction in effectivedensity thereof, agitating said crushed mixture while at elevatedtemperature to prevent agglomeration, separating the high vitrainparticles from the remaining particles, utilizing the difierences indensities of the mixed particles to effect such separation and mixingsaid separated high vitrain particles with particles of lower vitraincoals to form .a coking mixture; and heatingthe mixture to form a coke.

6. The method of separating high vitrain coal from a banded mixture ofcoal forms which comprises crushing said mixture to particle size notgreater than the minimum thickness of the included vitrain layers,heating the crushed mixture while in an inert atmosphere to atemperatureabove the initial softening point of the included vitrain and below thepoint of maximum fluidity thereof, agitating said crushed mixture whileat elevated temperature to prevent agglomeration, separating the highvitrain particles from the remaining particles, utilizing thedifferences in densities of the mixed particles to effect suchseparation, and utilizing at least a portion of the separatednon-vitrain coal to supply heat' for heating the crushed particles. 7

7. The method of separating high vitrain coal from a banded mixture ofcoal forms which comprises crushing said mixture to particle size notgreater than the minimum thickness of the included vitrain layers,subjecting the crushed mixture while in an inert atmosphere to atemperature above the initial softening point of the included vitrainand below the point of maximum fluidity to the action of a heatedfluidized column to thereby effect swelling of said high vitrainparticles and consequent reduction in efiective density thereof,agitation of said crushed mixture and separation of the high vitrainparticles from the remaining particles, utilizing the differences indensities of the mixed particles to effect such separation.

' No references cited.

1. THE METHOD OF SEPARATING HIGH VITRAIN COAL FROM A BANDED MIXTURE OFCOAL FORMS WHICH COMPRISES CRUSHING SAID MIXTURE TO PARTICLE SIZE NOTGREATER THAN MINIMUM THICKNESS OF THE INCLUDE VITRAIN LAYERS, HEATINGTHE CRUSHED MIXTURE WHILE IN AN INERT ATMOSPHERE TO A TEMPERATURE ABOVETHE INTIAL SOFTENING POINT OF THE INCLUDED VITRAIN ADD BELOW THE POINTOF MAXIMUM FLUIDITY THEREOFF THEREBY CAUSING SWELLING OF SAID HIGHVITRAIN PARTICULES AND CONSEQUENT REDUCTION IN EFFECTIVE DENSITYTHEREOF, MECHANICALLY AGITATING SAID CRUSHED MIXTURE WHILE AT ELEVATEDTEMPERATURE TO PREVENT AGGLOMERATION, AND UTILIZING THE RESULTINGDUFFERENCE IN DENSITY OF THE MIXED PARTICULES TO EFFECT SEPARATIONTHEREOF.